I changed number and ended my contract in December. Since then, I have been charged £12 every month. 

I've been in contact with customer service 3 times. Each time, they've told me it's been cancelled and to pay the final £12. Each time I get charged the next month. 

The whole company is a scam. They tell you they've cancelled but still charge and then you have to go through 2 hours of useless customer support.

Please make sure you don't sign up because you'll be paying for a SIM you no longer use.